A conventional ship employs a two-stroke cycle, low-speed diesel engine that ensures outputs at a low speed and can be driven by being directly coupled to a propeller.
Recently, NOx, SOx, and a natural gas of less amount of emission have attracted the attention as a fuel for the low-speed diesel engine. An injection of a high-pressure natural gas as the fuel to a combustion chamber of the low-speed diesel engine and burning of the high-pressure natural gas obtains the output at high thermal efficiency.
To boost the liquefied natural gas, for example, a reciprocating booster pump that includes a cylinder and a piston reciprocating at an inside of the cylinder is used (for example, see Japanese Patent No. 5519857). The cylinder has suction ports to suction a low-temperature liquid such as a liquefied natural gas to the inside and a discharge port to boost the low-temperature liquid and discharge the low-temperature liquid to an outside. The booster pump includes a suction check valve to open and close a suction flow passage between an internal space of the cylinder and the suction ports, and a discharge check valve to open and close a discharge flow passage between the internal space and the discharge port. The suction check valve is adjusted to open when a pressure at the internal space of the cylinder becomes smaller than a pressure of the low-temperature liquid before the boost. The discharge check valve is adjusted to open when the pressure at the internal space of the cylinder becomes higher than the pressure of the low-temperature liquid after the boost.